Environment regulators recommended Santos monitor radioactive elements in its future coal-seam gas operations in the Pilliga Forest despite not seeking such readings once unsafe levels of uranium were found in a contaminated aquifer.

On Tuesday, the Environment Protection Authority said it had not sought data on the levels of thorium, radon and radium - products of uranium - once Santos told it in March last year about leakage from a waste water pond. The aquifer was found to contain uranium at 20 times safe drinking levels and the EPA fined Santos $1500.

The three radioactive elements ''would only be tested for if there was an immediate threat to human health or the environment posed by the parent element uranium'', a spokeswoman for the EPA said. The decision that the site was safe was made within 24 hours of receiving the Santos-supplied results.

The readings ''should have rung alarm bells'', said Mariann Lloyd-Smith, a senior advisor for the National Toxics Network. ''It would have been sensible to go back and test the radioactivity of the water.''

Thorium and radon were known to cause lung cancer, she said, adding these materials could also spread by wind once the water they were suspended in evaporated.

However, internal emails from last August show the EPA's own water quality unit recommended Santos monitor ground water for ''radionuclides'', which include thorium, radon and radium.

The Wilderness Society's Naomi Hogan said the EPA should find out what the water already extracted contained. Clean-up efforts would result in water being pumped closer to the nearby town of Narrabri.